Photoperiodic Response of in vitro <em>Cannabis sativa </em>Plants

Abstract

Most commercial Cannabis sativa L. (cannabis) genotypes are short-day plants and cultivators typically use a 12.0 h uninterrupted dark period to induce flowering; however, scientific information is lacking to prove this is the optimal dark period for all genotypes, and cultivar specific photoperiods may increase productivity. Tissue culture can be used for research requiring multiple treatments, proper replication, and in a controlled environment on a smaller scale compared to greenhouse and indoor facilities. To determine whether cannabis explants can flower under varied photoperiods in vitro, explants were grown under one of six photoperiod treatments: 12.0, 13.2, 13.8, 14.4, 15.0, and 16.0 h for four weeks. The percentage of flowering explants was highest under 12.0 and 13.2 h treatments. There were no treatment effects on the fresh weight, final height, or growth index of the explants. The results suggest an uninterrupted dark period of at least 10.8 h (i.e. 13.2 h photoperiod) is needed to induce the flowering of this genotype. In vitro flowering could provide a unique and high throughput approach to study floral/seed development and secondary metabolism in cannabis under highly controlled conditions. Further research should determine if this response is the same on a whole plant level.

The Past, Present and Future of Cannabis sativa Tissue Culture

“…Leaves on a mature plant are digitate with anywhere from 5 to 11 leaflets and have a long petiole, although during flowering, they often revert to producing lower numbers of leaflets [ 23 , 28 ]. Cannabis is predominantly a short-day plant, with flowering induced by 12- to 14-h photoperiods [ 29 ]; however, some photoperiod-insensitive cultivars have been developed. Male and female plants cannot easily be distinguished until flowers begin to appear [ 26 , 30 ].…”

“…The maintenance of mother plants also requires them to remain in a vegetative state. While this is easily accomplished for most genotypes, it presents challenges for day-neutral genotypes as they do not respond to photoperiod [ 29 ]. Perhaps of greatest importance, though, is that mother plants are susceptible to insects, pathogens, and viruses and can transmit these biotic factors to their cuttings and lead to problems during production.…”

The Past, Present and Future of Cannabis sativa Tissue Culture

“…The inflorescence of the Cannabis plant is a highly branched compound racemose inflorescence that contains a large number of meristematic regions [22]. Initial observations found that some Cannabis plants initiate flower development in vitro ( Figure 1C and E), and recently Moher et al [29] demonstrated that flowering could be reliably induced using a short-day photoperiod similar to what is observed in the field. As such, in vitro flowering plants represent an alternative approach to increase the number of meristems per plant to potentially increase the multiplication rate.…”

“…Leaves on a mature plant are digitate with anywhere from 5-11 leaflets and have a long petiole, although during flowering they often revert to producing lower numbers of leaflets [23,28]. Cannabis is predominantly a short-day plant, with flowering induced by 12 to 14-hour photoperiods [29], however, some photoperiod insensitive cultivars have been developed. Male and female plants cannot easily be distinguished until flowers begin to appear [26,30].…”

“…The maintenance of mother plants also requires that they are maintained in a vegetative state. While this is easily accomplished for most genotypes, it presents challenges for day neutral genotypes as they do not respond to photoperiod [29]. Perhaps of greatest importance though, is that mother plants are susceptible to insect, pathogens, and viruses, and can transmit these biotic factors to their cuttings and lead to problems during production.…”